i just realized that there is an entire generation of e-mail users who use the word "CC" and have no idea what it means because the process it was modelled upon has disappeared.

Carbon Copy was a process used to make identical copies of writing (or typewriting) through one or more pieces of paper. it involved using a sheet of thin carbon paper in between two pieces of paper - as you wrote/typed on the top sheet, the carbon would imprint on the bottom sheet using pencil/pen pressure alone.

in the below image, the yellow sheet is the top sheet that you write on - there is a black sheet of carbon paper beneath it - and then a pink sheet that receives the copy below it. the customer gets the yellow sheet, the restaurant keeps the pink sheet.
there is a thin piece of cardboard (dark red) between that invoice and the next one, to prevent imprints from going through more than one layer.